\begin{tikzpicture}
    \pgfmathsetmacro{\a}{1.5}
    \pgfmathsetmacro{\b}{2}
    \begin{scope}
        \tkzDefPoints{0/0/A, \a/0/B, \a/\b/C, 0/\b/D}
        \tkzDrawPolygon(A,B,C,D)
        \tkzDrawSegment(A,C)
    \end{scope}

    \begin{scope}[xshift=2.5cm]
        \tkzDefPoints{0/0/A, \a/0/B, 2*\a/\b/C, \a/\b/D}
        \tkzDrawPolygon(A,B,C,D)
        \tkzDrawSegment(B,D)
    \end{scope}
\end{tikzpicture}

